1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a transflective liquid crystal display device and a fabricating method thereof.
2. Discussion of the Related Art
Generally, a transflective liquid crystal display (LCD) device functions both as a transmissive LCD device and a reflective LCD device. Transflective LCD devices are more versatile because they can use both a backlight and ambient light as light sources. Moreover, transflective LCD devices have low power consumption.
FIG. 1 is an exploded perspective view of an LCD device according to the related art. Referring to FIG. 1, a liquid crystal display (LCD) device 10 has an upper substrate 12 having a black matrix 17. A color filter layer 16 of the LCD device 10 includes sub-color filters. The LCD device 10 includes a common electrode 13 on the color filter layer 16, and a lower substrate 14 having a switching element, a thin film transistor (TFT) T, and a transparent electrode 20a connected to the TFT T. A liquid crystal material 18 is interposed between the upper and lower substrates 12 and 14. The lower substrate 14 is referred to as an array substrate because an array of lines, including gate lines 25 and data lines 27, is formed thereon. The gate lines 25 and the data lines 27 cross each other to form a matrix. The TFT T is connected to one of the gate lines 25 and one of the data lines 27. A pixel region P is defined between the gate lines 25 and the data lines 27. The TFT T is formed near a crossing of the gate lines 25 and the data lines 27. The transparent electrode 20a is formed of a transparent conductive material, such as indium-tin-oxide (ITO) and indium-zinc-oxide (IZO), in the pixel region P. The upper substrate 12 is referred to as a color filter substrate because the color filter layer 16 is formed thereon.
A reflective electrode 20b consisting of a reflective material, such as aluminum (Al) or Al alloy, is formed in the pixel region P. The reflective electrode 20b has a transmissive hole H so that the pixel region P is divided into a reflective portion D and a transmissive portion B. The transmissive portion B corresponds to the transmissive hole H and the reflective portion D corresponds to the reflective electrode 20b. 
The transflective LCD device is manufactured to selectively use a reflective mode, which depends on natural light, or a transmissive mode, which depends on a light source. The utilization efficiency of light is lower in the reflective mode than in the transmissive mode. Thus, brightness variation occurs in a transition from the reflective mode to the transmissive mode. To solve the problem, an uneven reflective layer is formed on the reflective portion in the related art LCD device to induce an irregular reflection by minimizing a specular-reflection of the incident ambient light and to improve brightness uniformity in the reflected mode and the transmissive mode.
FIG. 2 is a plan view of a pixel region of a transflective LCD device having an uneven reflective layer according to the related art. Referring to FIG. 2, a gate line 34 is formed on a substrate 30 along a first direction. A data line 46 crosses the gate line 34 to define a pixel region P. A thin film transistor T is formed near a crossing of the gate line 34 and the data line 46. The thin film transistor T includes a gate electrode 32, a semiconductor layer 41, a source electrode 42 and a drain electrode 44.
A transparent electrode 50 is formed in the pixel region P. The transparent electrode 50 is connected to the thin film transistor T. A reflective electrode 56 is also formed in the pixel region P. The reflective electrode 56 has a transmissive hole H that exposes the central portion of the transparent electrode 50.
A reflective portion D of the pixel region P corresponds to the transmissive hole H. A transmissive portion B of the pixel region P corresponds to the transparent electrode 50 excluding the reflective portion D. Specifically, the transparent electrode 50, which is located in the transmissive portion B and is connected to the drain electrode 44, generates a vertical field with respect to the common electrode 13 (shown in FIG. 1) through the liquid crystal layer 18 (shown in FIG. 1). The reflective electrode 56 reflects incident light.
The reflective layer is formed with an uneven surface to improve reflection efficiency. Thus, the brightness of the LCD device is improved and the viewing angle is widened. However, fabrication of the transflective LCD device increases the manufacturing complexity because of the additional mask process for forming the uneven reflective layer.
FIG. 3A is a cross-sectional view taken along line III-III of FIG. 2, showing a first mask process for fabricating a transflective LCD device according to the related art. Referring to FIG. 3A, a pixel region P is defined as a unit region for displaying an image. A switching device (shown in FIG. 2) is positioned in a switching region S on the substrate 30. The pixel region P includes a transmissive portion B and a reflective portion D. A gate line 34 (shown in FIG. 2) and a gate electrode 32 are formed using a metallic material having a low resistance on the substrate 30 through a first mask process. The gate electrode 32 is connected to the gate line 34.
Although not shown, the first mask process, which is a photolithography process, includes coating a photoresist on the metallic material layer, exposing the photoresist using a photo mask and developing the photoresist to form a photoresist pattern (not shown). The photoresist pattern is formed to shield the metallic material in a subsequent process. The first mask process further includes etching the metallic material using the photoresist pattern as a shield to pattern the gate line 34 (shown in FIG. 2) and the gate electrode 32. The steps of the first mask process can also be used in subsequent mask processes.
FIG. 3B is a cross-sectional view taken along line III-III of FIG. 2, showing a second mask process for fabricating a transflective LCD device according to the related art. Referring to FIG. 3B, a gate insulating layer 36 is formed using an inorganic insulating material over the entire surface of the substrate 30 including the gate line 34 (shown in FIG. 2) and the gate electrode 32 through a second mask process. An active layer 38 and an ohmic contact layer 40 are formed by patterning intrinsic amorphous silicon and impurity-doped amorphous silicon on the gate insulating layer 36 through the second mask process. In other words, the active layer 38 and the ohmic contact layer 40 are made of the intrinsic amorphous silicon and the impurity-doped amorphous silicon, respectively. The active layer 38 and the ohmic contact layer 40 constitute a semiconductor layer 41.
FIG. 3C is a cross-sectional view taken along line III-III of FIG. 2, showing third and fourth mask processes for fabricating a transflective LCD device according to the related art. Referring to FIG. 3C, a source electrode 42 and a drain electrode 44 are formed on the semiconductor layer 41 by a third mask process using a metallic material similar to that mentioned in FIG. 3A. A passivation layer 48 having a drain contact hole 49 that exposes the portion of the drain electrode 44 is formed by a fourth mask process using an organic or an inorganic insulating material over the entire surface of the substrate 30 having the source and drain electrodes 42 and 44.
FIG. 3D is a cross-sectional view taken along line III-III of FIG. 2, showing a fifth mask process for fabricating a transflective LCD device according to the related art. Referring to FIG. 3D, a transparent electrode 50 is formed through a fifth mask process using a transparent conductive material on the passivation layer 48. The transparent electrode 50 is connected to the drain electrode 44 via the drain contact hole 49.
FIG. 3E is a cross-sectional view taken along line III-III of FIG. 2, showing a sixth mask process for fabricating a transflective LCD device according to the related art. Referring to FIG. 3E, an organic insulating layer 51 is formed through a sixth mask process using an organic insulating material over the entire surface of the substrate 30 including the transparent electrode 50. The organic insulating material has good step-coverage property.
In the same mask process, a contact hole C1, a transmissive hole C2, and an uneven portion 52 are formed. The contact hole C1 exposes a portion of the transparent electrode 50. The transmissive hole C2 exposes a main portion of the transparent electrode 50 in the pixel region P. The uneven portion 52 is formed on the surface of the organic insulating layer 51 in the reflective portion D including the switching region S. The uneven portion 52 may be formed by melting the patterned organic insulating layer 51 that initially had a saw-tooth cross-section.
FIG. 3F is a cross-sectional view taken along line III-III of FIG. 2, showing a seven mask process for fabricating a transflective LCD device according to the related art. Referring to FIG. 3F, a reflective electrode 56 is formed through a seven mask process using a metallic material having good reflectivity. The reflective electrode 56 is formed over the substrate 30 including the unevenness 52. The reflective electrode 56 is located in the reflective portion D and is connected to the transparent electrode 50.
The related art fabricating method of the transflective LCD device has several problems. The mask processes are very complicated. Moreover, the production yield is reduced by the additional process for forming the uneven reflective pattern.